The most straight forward and least expensive way to build a supercomputer capable of executing hundreds of millions of instructions per second is to interconnect a large number of microprocessors. Commercially available supercomputers do not use this approach, but rely on very fast components and pipelined operations. However, such machines are quite expensive, and each performance improvement is increasingly difficult to achieve. In contrast, the performance of machines comprising interconnected microprocessors can be significantly improved by providing more microprocessors, faster microprocessors, and better interconnections between them. Recent advances in very large scale integrated (VSLI) circuit technology have produced fast, inexpensive single chip microprocessors which may be utilized to form computer systems comprising large numbers of such processors. Such computers are generally known as parallel processing computers because numerous instructions are executed in parallel, i.e., at the same time.
A typical parallel processing computer system comprises a plurality of processors, a plurality of memories and a cross-connect system for interconnecting the processors and memories. The cross-connect system is used to enable simultaneous and exclusive connections between specific processors and specific memories and should permit any processor to send a request to any memory and any memory to send a response to any processor.
An important problem in the physical design of parallel processing computers is the design of the cross-connect system. One prior art electronic cross-connect system utilizes a mesh of bus-like backplane structures. This has the disadvantage that the number of interconnecting wires increases as the product of the number of processors, the number of memories, and the bus bit-width. Such a cross-connect system is limited to a relatively small number of processors because of the wiring limitations alone.
Othe prior art electronic cross-connect systems for interconnecting processors and memories in a parallel processing computer include a non-blocking crosspoint switch architecture and a Banyan-type packet communication network architecture. The crosspoint switch has the drawback of growing like N.sup.2 for N processors. The Banyan-type structure has the drawback of a non-zero blocking probability and the drawback of an inherent processing delay while a path through the Banyan-type switching network is chosen. In general, electronic cross-connect systems require either parallel bus transmission or internal switches, and the large number of electrical wire connections seriously limits the maximum number of processors and the operational performance.
Optical networks have previously been implemented for interconnecting central offices in a telecommunications network. An example of such a network is disclosed in Cheung-Kobrinski-Loh U.S. patent application Ser. No. 948,244, abandoned, entitled "Multi-Wave Length Optical Telecommunication System", filed on Dec. 31, 1986 and assigned to the assignee hereof. The contents of this application are incorporated herein by reference. Each station or central office in the network of the above-described patent application comprises a transmitter capable of transmitting at a unique wavelength and a receiver. A hub element such as a passive star coupler is adapted to receive radiation at a different wavelength from each of the transmitters and transmit a fraction of the power received at each wavelength to all of the receivers. Thus, each central office receives a fraction of the power produced by each transmitter. The receiver at each central office is tunable to a specific wavelength so that simultaneous and exclusive connections can be established between particular central office pairs. Alternatively, the transmitters may be tunable and the receivers may be adapted to receive radiation of a fixed characteristic wavelength. Such optical networks have proven useful in overcoming some of the problems which arise in relation to the interconnection of central offices in a telecommunications network, including for example blocking problems, insufficient throughout problems, and physical design problems resulting from large numbers of wire cable connections.
Accordingly, efforts have been directed toward determining whether an optical system would be suitable for use as a cross-connect for a parallel computer. Thus, it is an object of the present invention to use passively coupled optical fibers and other optical components to provide an optical cross-connect for a parallel processing computer.